The state-of-the-art Fe/N/C catalyst has presented comparable initial cathode performance to the benchmark Pt/C catalyst in proton exchange membrane fuel cells(PEMFCs).However,the major bottleneck is its significant a...The state-of-the-art Fe/N/C catalyst has presented comparable initial cathode performance to the benchmark Pt/C catalyst in proton exchange membrane fuel cells(PEMFCs).However,the major bottleneck is its significant activity decay in real-world PEMFC cells.The superposed“fast decay”and“slow decay”have been well documented to describe the degradation process of Fe/N/C catalysts during PEMFC operation.The fast decay has been well understood in close relation to the demetallation at the initial 15-h stability test.Nevertheless,it is still unclear how the remanent active sites evolve after demetallation.To this end,the catalyst performance and evolution of a typical Fe/N/C active site were herein investigated through postmortem characterizations of the membrane electrode assemblies(MEAs)after different operations.It is presented that 1 bar pressure and 80℃ temperature are the optimized conditions for Fe/N/C MEA.Particularly,the“fast decay”in the initial 15 h is immune to the various operating parameters,while the“slow decay”highly depends on the applied temperature and pressure.According to the X-ray absorption spectra(XAS)analysis and stability test of MEA,the gradual evolution of Fe-N coordination to Fe-O is found correlated with the“slow decay”and accounts for the catalyst decay after the demetallation process.展开更多
Single-atom transition metal-nitrogen-doped carbons(SA M-N-Cs)catalysts are promising alternatives to platinum-based catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs).Howev...Single-atom transition metal-nitrogen-doped carbons(SA M-N-Cs)catalysts are promising alternatives to platinum-based catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs).However,enhancing their performance for practical applications remains a significant challenge.This review summarizes recent advances in enhancing the intrinsic activity of SA M-N-C catalysts through various strategies,such as tuning the coordination environment and local structure of central metal atoms,heteroatom doping,and the creation of dual-/multi metal sites.Additionally,it discusses methods to increase the density of M-Nx active sites,including chelation,defect capture,cascade anchoring,spatial confinement,porous structure design,and secondary doping.Finally,it outlines future directions for developing highly active and stable SA M-N-C catalysts,providing a comprehensive framework for the design of advanced catalysts.展开更多
Fe-N-C catalysts represent the most promising class of platinum group metal-free(PGM-free)catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs),exhibiting intrinsic activity po...Fe-N-C catalysts represent the most promising class of platinum group metal-free(PGM-free)catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs),exhibiting intrinsic activity potentially competitive with commercial Pt/C benchmarks.However,critical challenges persist[1].As revealed by theoretical calculations,the enhancement of intrinsic activity in Fe-N-C catalysts is constrained by inherent scaling relations among the adsorption free energies of ORR intermediates on the catalyst surface.展开更多
The drawbacks of conventional flow channel-rib flow fields and gas diffusion layers(GDLs)severely restrict mass transport and water management in proton exchange membrane fuel cells(PEMFCs),thereby limiting their volu...The drawbacks of conventional flow channel-rib flow fields and gas diffusion layers(GDLs)severely restrict mass transport and water management in proton exchange membrane fuel cells(PEMFCs),thereby limiting their volumetric power density.Our previous study proposed an ultrathin GDL-less PEMFC that uses metal foam to replace traditional flow fields and GDLs,significantly reducing mass transport distance and cell thickness while enhancing volumetric power density.To ensure contact and transition between the catalyst layer and metal foam,an ultrathin carbon nanofiber film(CNFF)is employed in this structure.This study systematically investigates the effect of CNFF thickness on the performance of ultrathin GDL-less PEMFCs.Results demonstrate that the protective effect of CNFF on the catalyst coated membrane(CCM)is strongly correlated with its thickness.Specifically,thinner CNFF offers less protection to the catalyst layer,resulting in an 30%difference in electrochemical active surface area(ECSA).A moderate increase in thickness reduces ohmic overpotential and enhances Knudsen diffusion within the oxygen catalyst layer,while excessive thickness leads to a decrease in oxygen molecular diffusion.Additionally,thicker CNFF provides better water storage and more effective water management under medium current densities,although performance degrades at ultrahigh current densities.Overall,the 25-μm CNFF balances these various factors to achieve the best integrated performance.These findings highlight that the optimal performance of GDL-less PEMFCs can be achieved by regulating the thickness of CNFF.展开更多
Covalent organic framework ionomers enable synergistic efficient transport of protons and oxygen in medium-temperature proton exchange membrane fuel cells Proton exchange membrane fuel cells(PEMFCs),as clean and effic...Covalent organic framework ionomers enable synergistic efficient transport of protons and oxygen in medium-temperature proton exchange membrane fuel cells Proton exchange membrane fuel cells(PEMFCs),as clean and efficient energy technologies,are constrained in their performance enhancement by the sluggish oxygen reduction reaction(ORR)kinetics at the cathode,anode CO poisoning(e.g.,from methanol crossover)and intricate water management dilemmas[1].展开更多
Design of catalyst layers(CLs)with high proton conductivity in membrane electrode assemblies(MEAs)is an important issue for proton exchange membrane fuel cells(PEMFCs).Herein,an ultrathin catalyst layer was constructe...Design of catalyst layers(CLs)with high proton conductivity in membrane electrode assemblies(MEAs)is an important issue for proton exchange membrane fuel cells(PEMFCs).Herein,an ultrathin catalyst layer was constructed based on Pt-decorated nanoporous gold(NPG-Pt)with sub-Debye-length thickness for proton transfer.In the absence of ionomer incorporation in the CLs,these integrated carbon-free electrodes can deliver maximum mass-specific power density of 198.21 and 25.91 kW·gPt^(-1) when serving individually as the anode and cathode,at a Pt loading of 5.6 and 22.0 pg·cm^(-2),respectively,comparable to the best reported nano-catalysts for PEMFCs.In-depth quantitative experimental measurements and finite-element analyses indicate that improved proton conduction plays a critical role in activation,ohmic and mass transfer polarizations.展开更多
基金financially supported by the Fundamental Re-search Funds for the Central Universities(No.2023CDJXY-016)the Outstanding Youth Project of Natural Science Foundation of Guangdong Province(Grant No.2022B1515020020).
文摘The state-of-the-art Fe/N/C catalyst has presented comparable initial cathode performance to the benchmark Pt/C catalyst in proton exchange membrane fuel cells(PEMFCs).However,the major bottleneck is its significant activity decay in real-world PEMFC cells.The superposed“fast decay”and“slow decay”have been well documented to describe the degradation process of Fe/N/C catalysts during PEMFC operation.The fast decay has been well understood in close relation to the demetallation at the initial 15-h stability test.Nevertheless,it is still unclear how the remanent active sites evolve after demetallation.To this end,the catalyst performance and evolution of a typical Fe/N/C active site were herein investigated through postmortem characterizations of the membrane electrode assemblies(MEAs)after different operations.It is presented that 1 bar pressure and 80℃ temperature are the optimized conditions for Fe/N/C MEA.Particularly,the“fast decay”in the initial 15 h is immune to the various operating parameters,while the“slow decay”highly depends on the applied temperature and pressure.According to the X-ray absorption spectra(XAS)analysis and stability test of MEA,the gradual evolution of Fe-N coordination to Fe-O is found correlated with the“slow decay”and accounts for the catalyst decay after the demetallation process.
基金supported by the National Natural Science Foundation of China(Grant No.22379123)the High-level Innovation and Entrepreneurship Talent Project from Qinchuangyuan of Shaanxi Province(Grant No.QCYRCXM-2022-226)+1 种基金the Key Research and Development Program of Shaanxi Province(Grant No.2024CY-GJHX-25)the National Natural Science Foundation of China,Pilot Group Program of the Research Fund for International Senior Scientists(Grant No.22250710676).
文摘Single-atom transition metal-nitrogen-doped carbons(SA M-N-Cs)catalysts are promising alternatives to platinum-based catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs).However,enhancing their performance for practical applications remains a significant challenge.This review summarizes recent advances in enhancing the intrinsic activity of SA M-N-C catalysts through various strategies,such as tuning the coordination environment and local structure of central metal atoms,heteroatom doping,and the creation of dual-/multi metal sites.Additionally,it discusses methods to increase the density of M-Nx active sites,including chelation,defect capture,cascade anchoring,spatial confinement,porous structure design,and secondary doping.Finally,it outlines future directions for developing highly active and stable SA M-N-C catalysts,providing a comprehensive framework for the design of advanced catalysts.
文摘Fe-N-C catalysts represent the most promising class of platinum group metal-free(PGM-free)catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs),exhibiting intrinsic activity potentially competitive with commercial Pt/C benchmarks.However,critical challenges persist[1].As revealed by theoretical calculations,the enhancement of intrinsic activity in Fe-N-C catalysts is constrained by inherent scaling relations among the adsorption free energies of ORR intermediates on the catalyst surface.
基金support from the National Natural Science Foundation of China for Distinguished Young Scholars(52225604)the Jilin Province Science and Technology Development Program(grant No.20230301017ZD)the Marine Defense Innovation Fund of China Ship Development and Design Center(Grant No.2023712-01).
文摘The drawbacks of conventional flow channel-rib flow fields and gas diffusion layers(GDLs)severely restrict mass transport and water management in proton exchange membrane fuel cells(PEMFCs),thereby limiting their volumetric power density.Our previous study proposed an ultrathin GDL-less PEMFC that uses metal foam to replace traditional flow fields and GDLs,significantly reducing mass transport distance and cell thickness while enhancing volumetric power density.To ensure contact and transition between the catalyst layer and metal foam,an ultrathin carbon nanofiber film(CNFF)is employed in this structure.This study systematically investigates the effect of CNFF thickness on the performance of ultrathin GDL-less PEMFCs.Results demonstrate that the protective effect of CNFF on the catalyst coated membrane(CCM)is strongly correlated with its thickness.Specifically,thinner CNFF offers less protection to the catalyst layer,resulting in an 30%difference in electrochemical active surface area(ECSA).A moderate increase in thickness reduces ohmic overpotential and enhances Knudsen diffusion within the oxygen catalyst layer,while excessive thickness leads to a decrease in oxygen molecular diffusion.Additionally,thicker CNFF provides better water storage and more effective water management under medium current densities,although performance degrades at ultrahigh current densities.Overall,the 25-μm CNFF balances these various factors to achieve the best integrated performance.These findings highlight that the optimal performance of GDL-less PEMFCs can be achieved by regulating the thickness of CNFF.
文摘Covalent organic framework ionomers enable synergistic efficient transport of protons and oxygen in medium-temperature proton exchange membrane fuel cells Proton exchange membrane fuel cells(PEMFCs),as clean and efficient energy technologies,are constrained in their performance enhancement by the sluggish oxygen reduction reaction(ORR)kinetics at the cathode,anode CO poisoning(e.g.,from methanol crossover)and intricate water management dilemmas[1].
基金financially supported by the National Natural Science Foundation of China(52073214,21603161,51671145,51761165012 and U1804255)the National Science Fund for Distinguished Young Scholars(No.51825102)the Tianjin Municipal Major Project of New Materials(No.16ZXCLGX00120).
文摘Design of catalyst layers(CLs)with high proton conductivity in membrane electrode assemblies(MEAs)is an important issue for proton exchange membrane fuel cells(PEMFCs).Herein,an ultrathin catalyst layer was constructed based on Pt-decorated nanoporous gold(NPG-Pt)with sub-Debye-length thickness for proton transfer.In the absence of ionomer incorporation in the CLs,these integrated carbon-free electrodes can deliver maximum mass-specific power density of 198.21 and 25.91 kW·gPt^(-1) when serving individually as the anode and cathode,at a Pt loading of 5.6 and 22.0 pg·cm^(-2),respectively,comparable to the best reported nano-catalysts for PEMFCs.In-depth quantitative experimental measurements and finite-element analyses indicate that improved proton conduction plays a critical role in activation,ohmic and mass transfer polarizations.
